This invention relates in general to brake drums and in particular to an improved method for balancing a brake drum.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system includes either a disc brake assembly or a drum brake assembly for each of the wheels. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. To effect braking action, frictional pads are moved against a braking surface formed in the brake disc or brake drum to frictionally engage therewith. The frictional engagement causes slowing or stopping of the rotational movement of the brake disc or brake drum and, therefore, the wheel of the vehicle in a controlled manner. The structure and operation of the brake assemblies, as well as the actuators therefor, are well known in the art.
There are various known methods of producing a brake drum. For example, brake drums can be formed by a conventional sand-patterned mold casting operation. After cleaning, the brake drum casting is precision drilled and concentrically machined to predetermined dimensional tolerances. For example, an inner cylindrical braking surface can be machined into the cast brake drum. Composite brake drums can be formed by stamping or rolling a generally cylindrical shell and then casting a liner in an inner surface of the shell. The composite brake drum undergoes an additional machining step in which the liner is machined to form a cylindrical inner braking surface.
After the drum brakes have been formed, they typically incorporate a sufficient imbalance which renders the brake drum unsatisfactory for use on a vehicle. As a result, the brake drum is generally subjected to a balancing operation. In the past, brake drums have been balanced by first determining the location and amount of the imbalance using a static balancer, and then welding correcting weights to an outer surface of the brake drum. Brake drums have also been balanced by removing material from a portion of the drum brake. For example, after the imbalance has been located by a static balancer, an operator marks the location of the imbalance on a squealer band of the drum. The squealer band is an integrally raised band formed about the outer surface of the drum. The drum is then transferred to a cutting machine which is operative to make a predetermined cut along a portion of the squealer band to thereby produce a balanced brake drum.
This invention is an improved method for producing a brake drum which balances a brake drum defining an inner surface and an axis. Balancing specifications are determined which correct an imbalance of the brake drum about the axis. The balancing specifications can be determined with the aid of a static balancer. The brake drum is then preferably transferred to a cutting machine where material is removed from the inner surface to balance the brake drum according to the balancing specifications. Preferably, the cutting machine forms a cylindrical surface in the brake drum which defines a braking surface of the brake drum. It is a further feature of the invention to remove material surrounding a pilot hole initially formed in the brake drum, wherein the removal of the material also correlates to the balancing specifications.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.